During the five robberies at the same store Dorsett, who wore a mask, made off with cash and packets of cigarettes.

He committed four robberies against the same 66-year-old man in Newtown, West Midlands Police said it discovered.

PC Sherrie Watkins, from the force's High Harm & Vulnerability Team, said: "Dorsett is a dangerous man…a bully who thinks nothing about carrying a knife in public and using it to threaten vulnerable people."

He was jailed at Birmingham Crown Court after admitting the 15 robberies and the count of assault with intent to rob between 10 November and 5 February.